Magnetic piston



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MAGNETIC PISTON I June 23, 197@ Filed Oct. 14, 1968 United States Patent O Int. Cl. Htllj 7,/24; H02n 4/00 U.S. Cl. 310-11 4 Claims ABSTRACT F THE DISCLOSURE An accelerator for plasmoids or metallic projectiles formed by a slotted cylinder and a tube within the cylin der. The edges of the slot, which runs the length of the cylinder, are connected to a current generator. The `tube is of varying cross-section-along its length and isspaced from the cylinder. When a magnetic field is '[produced by the cylinder, the tube volatilizes causing diffusion of the magnetic field to form a cusp-type magnetic iield.

The present invention relates to a novel device for accelerating plasmoids or ymetal projectiles. The device is based on the use of magnetic fields of confinement of cusp (pointed) type, whose end is propagated at high speed In its broad form the invention provides an accelerator for plasmoids or metallic projectiles comprising a tube of conductive material with a slot through itswalls extending from end to end, the edges of the slot being connected to -a current generator and a second tube within the first tube and spaced therefrom, the second tube also being of conductive material and having a cross-sectional material area which varies along the length ofthe tube.

More specifically the device according to the invention is characterised in that it provides a combination of a cylinder made of a conductive material which is slotted along la generatrix, the edges of the slot being connected to a current generator, and a second conductive cylinder whose wall thickness is not constant is disposed inside the first-mentioned cylinder coaxial therewith. In a pre= ferred embodiment of the invention, the Wall thickness of the second tube or cylinder progressively increases in the direction of propagation of the object to be accelerated.

The invention will be better understood with reference to the accompanying drawings, wherein:

FIG. 1 shows diagrammatically a prior art device;

FIG. 2 is a section, taken along an axial plane, through one example of a magnetic piston according to the invention; and

FIG. 3 is a transverse section through the piston shown in FIG. 2.

The device shown in FIG. 1 is a prior art LC circuit comprising inductances 1 in the form of coils disposed one after .the other in the direction of propagation vof the projectile to be accelerated, which passes axially inside the coils. The coils 1 are supplied by capacitors 2, 3. Switches 4, S complete the circuit, which can be used in various ways; 'j

(l) The capacitor 2 is charged, Whereafter the switch 4 is closed. A current pulse is then propagated along the whole line.

(2) All the capacitors are charged, whereafter they -are discharged to a predetermined program bythe switches 5 closed at the required moments.

These two methods share one limitation: for high values of dB/a't (B being the magnetic induction inthe coils), the induced electric ield V can no longer be supported by the coils, since for example if B is 0.5 megagauss and v l(speed of propagation of the pulse). is 107 cm./sec., the voltage per turn is of the order of l.6l()5 volts, this being the limit of what can be achieved in the present state of the art.

The device according to the invention shown in FIGS.'

2 and 3 allows more extreme conditions to be imposed.7 This mainly comprises a cylindrical or tubular conductor 6 slotted at a place 7 along one of its generatrices. The

resulting single-turn coil is connected at the edges of the slot viaa switch 8 to an accumulating device 9 which can be, for instance, a bank of capacitors, or any other known device.

Disposed inside the cylinder 6 coaxially therewith is a second cylinder or tube 10 which is also made of a con= ductive material and whose thickness increases in the required direction of propagation of the body to be accelerated, from the left to the right in the case illustrated in FIG. 2.

When the switch 8 is closed, the cylinder 6 produces a magnetic field B whose lines of' force are indicated by reference 11. The field B induces in the tube 10 currents which are dissipated in the tube I10 in the form of heat, the dissipation of heat causing the tube 10 to vaporize explosively after a short time interval. As thethickness of the tube 10 is not constant, the thinnest parts will vaporize rst, thus the cylinder 10 starts to be volatilized' on the left as shown in the figure, the volatilization being propagated from the left to the right. FIG.2 Vshows the device according to the invention when the front of the volatilization has reached the place 12. The part of the tube 10 which has already disappeared is shown in chain lines, the remaining part being shown in solid lines.

Clearly, the magnetic' field -B does not penetrate inside the cylinder 10, but the disappearance of the latter causes a sudden diffusion of the field into the space previously bounded by the cylinder 10, so that the lines of force 11 are curved very strongly inwards at the level of the disintegration front 12, so as to form a cusp type magnetic eld. The cusp is propagated from left to right along the front 12, thus enabling, the projectiles to be accelerated at the speed at which the front is propagated. In prin ciple, the speed can beinfinite. Clearly, the invention is not limited to the embodiment thereof described hereinbefore, but covers all variants; for instance, the speed of displacement of the front 12 can be regulated by varying the development of fthe thickness of the sheet or tube 10. Another Iway of regulating the speed is to regulate the intensity of the magnetic field B.

I claim: '51

1. An accelerator foi plasmoids or metallic projectiles comprising a tube of conductive material having a longi tudirral slot through its wall extending from end to end, means to apply current from a current generator to the edges of the slot to produce an axial flux therein, and a ,second tube within the first tube and spaced therefrom,

the second tube being of conductive material and having a cross-sectional area which varies along the length of the second tube, the dimensions of said second tube being such that it is heated by current induced therein by said flux until vaporization temperature is reached when it will commence to vaporize thereby forming a cusp-type mag netic field.

2. An accelerator as claimed in .claim l wherein the cross-sectional area of said inner tube increases along the length of the tube in the direction of propagation of the body to be accelerated.

3. A magnetic piston for accelerating plasmoids or metal projectiles comprising, in combination, a cylinder of conductive material which is slotted along a generatrix, means for applying current from a current generator to the edges of said slot to produce an axial fiux in said cylin-l der, and a second cylinder of conductive material coaxially mounted withinl said first cylinder, said second cylinder having a wall thickness that increases along the length thereof and being so dimensioned that it is heated by current induced therein by said ux until vaporization temperature is reached when it will commence to vaporize progressively from its smallest thickness thereby forming a cusp-type magnetic field.

4 A magnetic piston as claimed in claim 3 wherein said Wall thickness of said second cylinder progressvely lo 4 References Cited UNITED STATES PATENTS 6/1959 Kilpatrick 313-63 5/1967 Phillips et al. 315-111 DAVID X. SLINEY, Primary Examiner U.S. Cl. X.R 

